In the first clinical study of a new blood protein
associated with prostate cancer, researchers have found
that the marker, called EPCA or early prostate cancer
antigen, can successfully detect prostate cancer in its
earliest stages.
At the same time, the marker successfully avoids the
problem of false positive results that plagues
prostate-specific antigen testing.
Study results appear in the May 15 issue of Cancer
Research. The lead author is Robert H. Getzenberg,
professor of urology and director of research at the
James Buchanan
Brady Urological Institute at Johns Hopkins.
The traditional two-step approach of PSA testing and
digital rectal examination has helped doctors identify
prostate tumors early, while the cancers can still be
cured. But PSA testing, like many disease-screening
procedures, misses some cases of cancer and in other cases
erroneously highlights noncancerous conditions.
"This new blood test, when coupled with PSA screening,
may help reduce the number of both unnecessary biopsies and
undetected prostate tumors," Getzenberg said. In addition
to being highly sensitive to prostate cancer, the EPCA test
is very specific to it, meaning that other cancers and
benign prostate conditions are not detected, thus boosting
doctors' confidence that a positive EPCA test is really a
sign of prostate cancer, Getzenberg added.
"Once this test is refined and approved for general
use, it will have an impact on the detection and treatment
of prostate cancer," Getzenberg said.
For the current study, Getzenberg and colleagues
developed a simple test that would detect EPCA in the blood
and then measured the EPCA levels in 46 patients, including
those with prostate cancer (12 patients), bladder cancer
(six patients), colon cancer (two patients), kidney cancer
(one patient), spinal cord injury (seven patients) and
noncancerous prostate inflammation (two patients) and 16
healthy individuals. The study was conducted at the
University of Pittsburgh while Getzenberg was a member of
its faculty.
The researchers found that EPCA levels were high in 11
of 12 prostate cancer patients (92 percent) and low in all
the healthy individuals. Only two bladder cancer patients
and none of the other patients had elevated EPCA levels,
suggesting that for this study, the test was correct 94
percent of the time. In comparison, only one-quarter of
patients who undergo biopsies because they have elevated
PSA values are actually positive for prostate cancer, while
as many as 15 percent of those with low PSA values were
found to have prostate cancer as detected by biopsy,
according to Getzenberg.
Larger clinical trials are under way to further refine
the EPCA test, to make it more sensitive so it can pick up
even the smallest traces of the marker and to verify its
usefulness for detecting prostate cancer in a larger sample
of patients, Getzenberg said.
Prostate cancer is the most common type of cancer
found in American men. The American Cancer Society
estimates that there will be approximately 232,090 new
cases of prostate cancer in the United States in 2005 and
that 30,350 men will die of this disease.
Funding for the study was provided by Tessera. Other
authors on the report are Barbara Paul, Rajiv Dhir, Douglas
Landsittel and Moira Hitchens, all of the University of
Pittsburgh.
Robert Getzenberg is a paid consultant to and received
an unrestricted research grant from Tessera. Under separate
agreements between the University of Pittsburgh and Tessera
and The Johns Hopkins University and Tessera, Getzenberg is
entitled to a share of royalty payments to the universities
on sales of licensed products. The EPCA test is the subject
of the license agreement between the University of
Pittsburgh and Tessera.
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